High concentrations of heavy metals in neighborhoods near ore smelters in northern Mexico

In developing countries, rapid industrialization without environmental cont rols has resulted in heavy metal contamination of communities. We hypothesi zed that residential neighborhoods located near ore industries in three nor thern Mexican cities would be heavily polluted with multiple contaminants ( arsenic, cadmium, and lead) and that these sites would be point sources for the heavy metals. To evaluate these hypotheses, we obtained samples of roa dside surface dust from residential neighborhoods within 2 m of metal smelt ers [Torreon (n = 19)] and Chihuahua (n = 19)] and a metal refinery [Monter rey (It = 23)]. Heavy metal concentrations in dust were mapped with respect to distance from the industrial sites. Correlation between dust metal conc entration and distance was estimated with least-squares regression using lo g-transformed data. Median dust arsenic, cadmium, and lead concentrations w ere 32, 10, and 277 mu g/g, respectively, in Chihuahua; 42, 2, and 467 mu g /g, respectively, in Monterrey, and 113, 112, and 2,448 mu g/g, respectivel y, in Torreon. Dust concentrations of all heavy metals were significantly h igher around the active smelter in Torreon, where more than 90% of samples exceeded Superfund cleanup goals. Ar all sites, dust concentrations were in versely related to distance from the industrial source, implicating these i ndustries as the likely source of the contamination. We concluded that resi dential neighborhoods around metal smelting and refining sites in these thr ee cities are contaminated by heavy metals at concentrations likely to pose a health threat to people living nearby. Evaluations of human exposure nea r these sires should be conducted. Because multiple heavy metal pollutants may exist near smelter sites, researchers should avoid attributing toxicity to one heavy metal unless others have been measured and shown not to coexi st.